There has been an ammonia engine using ammonia as fuel. Because the ammonia engine has a characteristic that ignition performance is poor, combustion of ammonia becomes insufficient during low load operation and high load operation of the engine. It is therefore necessary for the ammonia engine to add a combustion improver to promote combustion of ammonia. Hydrocarbon fuel and hydrogen are available as the combustion improver. Ammonia is a compound of hydrogen atoms and a nitrogen atom and it is possible to produce hydrogen by chemically cracking ammonia. The ammonia engine is therefore thought to be the most desirable system in that the engine can be driven by ammonia alone by using hydrogen produced by cracking ammonia as the combustion improver.
A reaction to produce hydrogen and nitrogen from ammonia with an ammonia cracking catalyst is an endothermic reaction. In order to allow this reaction to progress, it is necessary to bring the ammonia cracking catalyst into contact with ammonia while conferring a temperature of 290° C. or above (preferably 340° C. or above) to the ammonia cracking catalyst.
Patent Document 1 discloses an ammonia combustion engine configured to supply ammonia cracking means with an exhaust gas after combustion of ammonia in the ammonia combustion engine.
This ammonia combustion engine promotes a cracking reaction of ammonia by utilizing the fact that an ammonia-containing exhaust gas becomes hot due to combustion in the ammonia combustion engine.
In this device, however, the temperature of the ammonia cracking catalyst depends on the temperature of the exhaust gas. Accordingly, combustion efficiency of ammonia in the ammonia engine is poor during low load operation (engine start-up) and a hot exhaust gas is not supplied to the ammonia cracking catalyst. Hence, a reaction to produce hydrogen and nitrogen from ammonia progresses poorly. Consequently, hydrogen serving as a combustion improver to promote the driving of the engine is not supplied to the ammonia combustion engine in a low load operating condition. It therefore takes a long time for the ammonia engine to come out of the low load operating condition.
Patent Document 1: JP-A-5-332152